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Some questions around efficacy and effectiveness

Some questions around efficacy and effectiveness. Gus Cairns NAM Publications www.aidsmap.com. Efficacy and effectiveness…. Efficacy is intervention use under perfect conditions Can be determined for some interventions, eg a vaccine

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Some questions around efficacy and effectiveness

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  1. www.guscairns.com Some questions around efficacy and effectiveness Gus Cairns NAM Publications www.aidsmap.com

  2. Efficacy and effectiveness… • Efficacy is intervention use under perfect conditions • Can be determined for some interventions, eg a vaccine • Can’t be (easily) determined where user choice continues to be crucial to effect of intervention, e.g. coitally-dependent interventions • Effectiveness, in my book, is the actual effect the intervention has in reducing infections in a specific population • Very difficult to determine because requires longitudinal measurements of HIV (or STI) incidence – most studies of interventions too small, especially behavioural ones. So we measure risks rather than events. www.guscairns.com

  3. And something in between… • Microbicide, PrEP, condom studies are something in between: effectiveness, but under conditions designed to maximise use of intervention • Effectiveness seen may therefore be a maximum: people will probably use it less than in the trial • Only likely to underestimate efficacy if trial designed so that ‘standard of care’ offered (ethically necessary) isn’t really standard of care, e.g. free condoms where there were none before. Efficacy in these cases is obscured by adoption of S-O-C www.guscairns.com

  4. What already happens • In UK slightly under 50% of gay men are ‘always’ or consistent condom users • Efficacy of condoms under attempted 100% use = c 85%* • Effectiveness therefore in the region of 42.5%. *Davis KR and Weller SC. The Effectiveness of Condoms in Reducing Heterosexual Transmission of HIV. Fam Plann Perspect. 31(6):272-279. 1999. www.guscairns.com

  5. Real-world usage www.guscairns.com

  6. Influences on condoms… • A risk has to be seen as a risk • Condom use (and therefore NPTs???) is usually lower in long-term relationships • Unprotected sex is not necessarily unsafe sex (serosorting etc) • Risk populations change - prevention targets must, too • Men can change... • ...but women can't always make them www.guscairns.com

  7. Influences on availability and effectiveness in real world • Social position of group to which NPT is offered (stigma etc: do they ‘deserve’ it?) • Social desirability or undesirability – am I bad for using this? • Personal desirability or undesirability – is it fun or yucky? • Emotional desirability or undesirability – does it imply mistrust/lack of intimacy? www.guscairns.com

  8. Influences on availability and effectiveness in real world – part 2 • Accurate understanding of NPT effect and efficacy • Public or private provision: OTC or prescribed? • Public view of what intervention ‘ought’ to do: • ‘Should’ an HIV vaccine be near-100% effective (eg polio, HPV) or is partial efficacy OK? (eg flu) • Should an OTC intervention be more effective (because people are paying for it and there are even more rigorous safety requirements (eg Voltarol)… • Or is it OK to be less effective because the state is not paying for it and it’s their choice (eg complementary medicines)? • COST!! www.guscairns.com

  9. Ethical background • Post-trial ethics • Is HIV these days a sufficiently lethal condition that offering partially-protective NPT is unethical? At what efficacy threshold? • How you market-describe it: unethical to overstate efficacy, even by implication • What if your info is as good as possible but people still misunderstand/misuse it? • Because people don’t calculate sexual risk rationally/cognitively • Because it ‘frees’ them to adopt a riskier but more pleasurable behaviour? • Because it damps down demand for safer but more expensive NPTs? www.guscairns.com

  10. What will work • Has to cause less psychological distress than the thought of not using it (eg vaccine causes very little: condoms cause a significant amount: what would microbicides do?) • Social desirability and peer groups • Stigma/bureaucracy met with in requesting intervention (this worries me about PrEP: would happen with anal-specific microbicide too?) • Powerful influence of individual campaigners • UK PEP story • Co-packaging NPTs with risk factors (eg put tenofovir in Viagra!) www.guscairns.com

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